Human interleukin 5 (IL-5) is a lineage-specific cytokine released mainly from activated T cells. Sanderson, 1992, Blood 79:3101-3109. Takatsu et al., 1988, Immunol. Rev. 102:107-135. A number of studies have demonstrated that IL-5 is responsible for the differentiation, proliferation and maturation of eosinophils from their progenitors in the bone marrow. Saito et al., 1988, Proc. Natl. Acad. Sci. USA 85:2288-2392. Lopez et al., 1988, J. Exp. Med. 167:219-224. Clutterbuck and Sanderson, 1988, Blood 71:646-658. Clutterbuck et al., 1989, Blood 73:1504-1512. Ema et al., 1990, Blood 76:1956-1961.
IL-5, Interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF) exhibit similar functions on eosinophils in vitro. Clutterbuck et al., 1989, Blood 73:1504-1512. Ema et al., 1990, Blood 76:1956-1961. However, whereas the action of human IL-5 is restricted to eosinophil and closely related basophil lineages (Sanderson, 1992 Blood 79:3101-3109), IL-3 and GM-CSF also have activities on other hematopoietic lineages. Miyajima et al., 1993, Blood 82:1960-1974.
IL-5 mediates its activity through a cell membrane receptor complex. This complex has been characterized physicochemically in both the murine and human systems. Mita et al., 1989, Proc. Natl. Acad. Sci. USA. 86:2311-2315. Plaelinck et al., 1990, J. Exp. Med. 172:623-691. Two receptor proteins, with molecular masses closely resembling those of murine IL-5 receptor .alpha.- and .beta.-chains (mIL-5R.alpha. and mIL-5R.beta.) are involved in the binding of human IL-5 (hIL-5). The .alpha.-chain (60 kd component) corresponds to the low affinity IL-5 binding site (K.sub.d =10.sup.-9 M). The .beta.-chain (130 kd component) associates with the .alpha.-chain to form the high affinity binding site (K.sub.d =2.5.times.10.sup.-10 M). Tavernier et al., 1991, Cell 66:1175-1184. Miyajima et al., 1993, Blood 82:1960-1974. High affinity human IL-5 receptors (hIL-5R) have been found in eosinophils and their related cell lines. Migita et al., 1991, Cell. Immunol. 133:484-497; Ingley and Young, 1991, Blood 78:339-344.
The cDNAs encoding the human .alpha.-chain component (hIL-5R.alpha.) and the human .beta.-chain component (hIL-5.beta.) have been cloned and characterized. Tavernier et al., 1991, Cell, 66:1175-1184. Murata et al., 1992, J. Exp. Med. 175:341-351. Hayashida et al., 1990, Proc. Natl. Acad. Sci. USA 87:9655-9659. The .alpha. subunit is responsible for IL-5 binding specificity and is distinct from the IL-3R.alpha. subunit and the GM-CSFR.alpha. subunit. Consistent with the studies of receptor binding assays, Northern blot experiments also have demonstrated that the expression of IL-5R.alpha. mRNA is restricted to eosinophils and their related cell lines. The .beta. subunit is shared by IL-3R and GM-CSFR and is essential for both the formation of high-affinity receptor complexes and signal transduction. Miyajima et al., 1993, Blood 82:1960-1974. Nucleotide sequencing and binding experiments show that the .beta. receptor component is identical to the .beta.-chain component of human GM-CSFR. Tavernier et al., 1991, Cell 66:1175-1184. Takaki et al, 1993, J. Exp. Med. 177:1523-1529. The cell type specific expression of the IL-5R.alpha. chain appears to be a required and crucial factor for the specific roles of IL-5 to these cells. Miyajima et al., 1993, Blood 82:1960-1974.
The process of eosinophilopoiesis is increased in certain disease states. Eosinophilia is characteristic of most parasitic infections as well as other disorders including dermatoses, allergies, polyarteritis nodosa and neoplastic diseases. Bronchial eosinophilia is a cardinal feature of chronic asthma. Multiple lines of evidence indicate that overexpression of IL-5 plays a crucial role in a number of eosinophil-related diseases. Owen et al., 1989, J. Exp. Med. 170:343-348. Owen et al., 1990, Proc. Natl. Acad. Sci. USA 87:8647-8651.
A central and specific role of IL-5 in controlling eosinophil functions in vivo was suggested by studies that mice bearing an IL-5 transgene produce a specific eosinophilia. Vaux et al., 1990, Int. Immunol. 2:965-970. Dent et al., 1990, J. Exp. Med. 172:1425-1431. Limaye et al., 1990, J. Exp. Med. 172:399-402. Moreover, antibodies specific to IL-5 inhibit eosinophil production induced by parasites and pathological stimuli. Coffman et al., 1989, Science 245:308-310. Gulbenkian et al., 1992, Am. Rev. Respir. Dis. 146:263-265. Ohnishi et al., 1993, Am. Rev. Respir. Dis. 147:901-907. A selective enhancement of IL-5 production was demonstrated in human helminth-infected patients with eosinophilia and in eosinophilic mice infected with Toxocara canis. Limaye et al., 1990, J. Exp. Med. 172:399-402 and Yamaguchi et al. 1990, Exp. Hematol. 18:1152-1157, respectively.
There is a need in the art to find therapeutic compounds useful in the treatment of chronic asthma and other IL-5-based disorders and disease states with demonstrated eosinophilia. There thus is a need for an expression system capable of expressing high affinity IL-5R at high levels and methods that can be used to identify receptor-based IL-5 antagonists potentially useful as therapeutic agents.